<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript" src="./js/ctx.js"></script>
</head>
<body>
<div id="cesiumContainer">
</div>
<script>
    var initCesium = new InitCesium();
    var viewer = initCesium.initViewer('cesiumContainer', {
        vrButton: true,
        terrainProvider: Cesium.createWorldTerrain()
    });
    // Click the VR button in the bottom right of the screen to switch to VR mode.

    viewer.scene.globe.enableLighting = true;
    viewer.scene.globe.depthTestAgainstTerrain = true;

    // Follow the path of a plane. See the interpolation Sandcastle example.
    Cesium.Math.setRandomNumberSeed(3);

    var start = Cesium.JulianDate.fromDate(new Date(2015, 2, 25, 16));
    var stop = Cesium.JulianDate.addSeconds(start, 360, new Cesium.JulianDate());

    viewer.clock.startTime = start.clone();
    viewer.clock.stopTime = stop.clone();
    viewer.clock.currentTime = start.clone();
    viewer.clock.clockRange = Cesium.ClockRange.LOOP_STOP;
    viewer.clock.multiplier = 1.0;
    viewer.clock.shouldAnimate = true;

    function computeCirclularFlight(lon, lat, radius) {
        var property = new Cesium.SampledPositionProperty();
        var startAngle = Cesium.Math.nextRandomNumber() * 360.0;
        var endAngle = startAngle + 360.0;

        var increment = (Cesium.Math.nextRandomNumber() * 2.0 - 1.0) * 10.0 + 45.0;
        for (var i = startAngle; i < endAngle; i += increment) {
            var radians = Cesium.Math.toRadians(i);
            var timeIncrement = i - startAngle;
            var time = Cesium.JulianDate.addSeconds(start, timeIncrement, new Cesium.JulianDate());
            var position = Cesium.Cartesian3.fromDegrees(lon + (radius * 1.5 * Math.cos(radians)), lat + (radius * Math.sin(radians)), Cesium.Math.nextRandomNumber() * 500 + 1800);
            property.addSample(time, position);
        }
        return property;
    }

    var longitude = -112.110693;
    var latitude = 36.0994841;
    var radius = 0.03;

    var modelURI = '../data/models/CesiumBalloon/CesiumBalloon.glb';
    var entity = viewer.entities.add({
        availability : new Cesium.TimeIntervalCollection([new Cesium.TimeInterval({
            start : start,
            stop : stop
        })]),
        position : computeCirclularFlight(longitude, latitude, radius),
        model : {
            uri : modelURI,
            minimumPixelSize : 64
        }
    });

    entity.position.setInterpolationOptions({
        interpolationDegree : 2,
        interpolationAlgorithm : Cesium.HermitePolynomialApproximation
    });

    // Set initial camera position and orientation to be when in the model's reference frame.
    var camera = viewer.camera;
    camera.position = new Cesium.Cartesian3(0.25, 0.0, 0.0);
    camera.direction = new Cesium.Cartesian3(1.0, 0.0, 0.0);
    camera.up = new Cesium.Cartesian3(0.0, 0.0, 1.0);
    camera.right = new Cesium.Cartesian3(0.0, -1.0, 0.0);

    viewer.scene.postUpdate.addEventListener(function(scene, time) {
        var position = entity.position.getValue(time);
        if (!Cesium.defined(position)) {
            return;
        }

        var transform;
        if (!Cesium.defined(entity.orientation)) {
            transform = Cesium.Transforms.eastNorthUpToFixedFrame(position);
        } else {
            var orientation = entity.orientation.getValue(time);
            if (!Cesium.defined(orientation)) {
                return;
            }

            transform = Cesium.Matrix4.fromRotationTranslation(Cesium.Matrix3.fromQuaternion(orientation), position);
        }

        // Save camera state
        var offset = Cesium.Cartesian3.clone(camera.position);
        var direction = Cesium.Cartesian3.clone(camera.direction);
        var up = Cesium.Cartesian3.clone(camera.up);

        // Set camera to be in model's reference frame.
        camera.lookAtTransform(transform);

        // Reset the camera state to the saved state so it appears fixed in the model's frame.
        Cesium.Cartesian3.clone(offset, camera.position);
        Cesium.Cartesian3.clone(direction, camera.direction);
        Cesium.Cartesian3.clone(up, camera.up);
        Cesium.Cartesian3.cross(direction, up, camera.right);
    });

    // Add a few more balloons flying with the one the viewer is in.
    var numBalloons = 12;
    for (var i = 0; i < numBalloons; ++i) {
        var balloonRadius = (Cesium.Math.nextRandomNumber() * 2.0 - 1.0) * 0.01 + radius;
        var balloon = viewer.entities.add({
            availability : new Cesium.TimeIntervalCollection([new Cesium.TimeInterval({
                start : start,
                stop : stop
            })]),
            position : computeCirclularFlight(longitude, latitude, balloonRadius),
            model : {
                uri : modelURI,
                minimumPixelSize : 64
            }
        });

        balloon.position.setInterpolationOptions({
            interpolationDegree : 2,
            interpolationAlgorithm : Cesium.HermitePolynomialApproximation
        });
    }



</script>
</body>
</html>